Estimating information about an antenna system, based on propagation-time measurements that are provided by wireless terminals

ABSTRACT

A location engine that accounts for propagation-time components in an antenna system disposed between i) the base station that serves a wireless terminal and ii) the airwaves over which electromagnetic signals propagate between the antenna elements and wireless terminal. By considering and accounting for these propagation components, the location engine is able to estimate information about the antenna system, such as i) whether the antenna system is a distributed antenna system and ii) the configuration of the antenna system. Based on this estimated information, the location engine is also able to estimate adjustments that can be made to location-related measurements, and, with these adjustments, estimate the location of one or more wireless terminals.

FIELD OF THE INVENTION

The present invention relates to telecommunications in general, and,more particularly, to a technique for estimating information about anantenna system in a wireless telecommunications system that comprisesone or more distributed antennas, based on propagation-time measurementsthat are provided by wireless terminals.

BACKGROUND OF THE INVENTION

The salient advantage of wireless telecommunications over wirelinetelecommunications is that the user of the wireless terminal is affordedthe opportunity to use his or her terminal anywhere. On the other hand,the salient disadvantage of wireless telecommunications lies in thatfact that because the user is mobile, an interested party might not beable to readily ascertain the location of the user.

There are many techniques in the prior art for estimating the locationof a wireless terminal. In accordance with some techniques, the locationof a wireless terminal is estimated, at least in part, from measurementsthat are reported by the wireless terminal. The reported measurementsare of signals measured by the wireless terminal that are transmitted byone or more base stations through their antennas and, in some cases, byGlobal Positioning System (GPS) satellites. Some techniques rely onsignal-strength measurements, while some other techniques rely ontime-based measurements, while still some other techniques rely on othertypes of measurements. In order for these estimation techniques to work,at least some of the transmitted signals have to be strong enough toallow for accurate measurement by the wireless terminal and for reliableprocessing by the particular technique.

A number of these techniques need to know which infrastructureantenna—as distinguished from the wireless terminal's antenna—radiatesthe signal that is received and decoded by the wireless terminal. Aninfrastructure antenna can be present in a variety of configurations;for example, it can be collocated with and coupled directly to a basestation, or can be part of a distributed antenna system (DAS), or can bepart of another type of antenna system (e.g., a repeater, etc.). Inwireless telecommunications systems without distributed or repeaterantennas, determining which infrastructure antenna radiates which signalis generally straightforward because each signal is uniquely associatedwith one infrastructure antenna. Therefore, the decoding andidentification of a signal is tantamount to the identification of theinfrastructure antenna that radiated the signal.

In wireless telecommunications systems that comprise distributed antennasystems, however, the decoding and identification of a signal does notinherently indicate which infrastructure antenna radiated it. Therefore,the need exists for a technique for estimating information aboutdistributed antenna systems that are present within a wirelesstelecommunication system, whereupon the information can be used forestimating the location of a wireless terminal or for other purposes.

SUMMARY OF THE INVENTION

The present invention enables estimation of information related to adistributed antenna system (DAS), or to another antenna system havingmultiple elements that radiate the same signal, and estimation of thelocation of a wireless terminal in the presence of a DAS, without someof the costs and limitations associated with techniques for doing so inthe prior art.

Typically, there are multiple propagation-time components in atransmission path between a base station and a wireless terminal in acoverage area being served by a wireless telecommunications system. Onesuch propagation component is in the antenna system (e.g., a distributedantenna system, etc.) that is disposed between i) the base station thatserves a wireless terminal and ii) the airwaves over whichelectromagnetic signals propagate between the antenna elements (nodes)and wireless terminal.

A location engine of the illustrative embodiment accounts for theafore-described propagation component, and other propagation componentsas well, through the use of measurement data provided by one or morewireless terminals. By considering and accounting for these propagationcomponents, the location engine disclosed herein is able to estimateinformation about the antenna system, such as i) whether the antennasystem is a distributed antenna system and ii) the configuration of theantenna system. Based on this estimated information, the location engineis also able to estimate adjustments that can be made tolocation-related measurements, and, with these adjustments, estimate thelocation of one or more wireless terminals.

In accordance with the illustrative embodiment of the present invention,the location engine, implemented on a server computer or other computingdevice, receives propagation-time measurements of signals between a basestation and a wireless terminal in a coverage area being served by thebase station, for one or more wireless terminals and/or base stations.For example and without limitation, a propagation-time measurement canbe the round-trip time (RTT) measurement made and reported by wirelessterminals in certain third-generation (3G) cellular networks. Thelocation engine can use many data points that are provided by eachwireless terminal or provided by potentially many wireless terminals,thereby leveraging a crowdsourced effect.

The illustrative location engine builds and maintains one or more datasets over time, wherein each data set is made up of values that arebased on the propagation-time measurements. When the data set issufficiently large, the location engine generates a statistic of thedata set. In at least some embodiments of the present invention, thestatistic summarizes i) a measure of location of one or more groupingsof data points within the data set (e.g., mean, median, predeterminedpercentile, etc.), wherein each grouping is defined by a local maximum,ii) a measure of statistical dispersion within the grouping (e.g.,standard deviation, range, etc.), or iii) a measure of the shape of thedistribution of the grouping (e.g., skewness, etc.), for example andwithout limitation.

The illustrative location engine then uses the statistic to estimate acharacteristic of an antenna system that is communicatively coupled to abase station. The characteristic can represent one or more of thefollowing, for example and without limitation:

-   -   a. whether the antenna system is a distributed antenna system,    -   b. the number of antenna nodes in the antenna system,    -   c. a cable delay between a predetermined antenna node and a        predetermined component of the base station (e.g., a radio        transceiver, etc.),    -   d. whether a predetermined antenna node is serving a particular        wireless terminal.

In some embodiments of the present invention, the illustrative locationengine then estimates the location of one or more wireless terminalsbased on the estimated characteristic. For example and withoutlimitation, the location engine can use the characteristic in order to:

-   -   a. adjust one or more propagation-time measurements based on a        cable-delay characteristic,    -   b. infer evidence of a location based on a cable-delay        characteristic,    -   c. infer evidence of a location based on having estimated        whether a particular antenna node is serving a particular        wireless terminal,    -   d. designate at least one of a plurality of possible locations        of a wireless terminal as improbable based on whether an antenna        node is serving the wireless terminal,

The disclosed techniques are advantageous, at least in part because theyenable a location estimation system to resolve at least some of theambiguity about a multiple-element antenna system that is involved insignal transmissions, including determining the radiating antennaelement of a signal component that is detected and measured by awireless terminal, and used by the system. As a result, the location ofa wireless terminal can be estimated more accurately.

In various embodiments of the present invention, a distributed antennasystem (DAS) is featured as an antenna system that comprises multipleantenna elements that transmit the same signal. In other embodiments ofthe present invention, a different type or types of antenna system canbe used, as those who are skilled in the art will appreciate afterreading this specification. Furthermore, although a location engine isfeatured in this specification, a different element that embodies thefeatures disclosed herein can be used, as those who are skilled in theart will appreciate after reading this specification.

A first illustrative method comprises: receiving, by a server computer,a plurality of propagation-time measurements of first signalstransmitted between i) one or more wireless terminals and ii) a basestation, wherein the first signals propagate through at least a portionof an antenna system that is communicatively coupled to the basestation; generating a statistic, by the server computer, by applying apredetermined statistical algorithm to a data set, wherein the data setcomprises data points that are based on the plurality ofpropagation-time measurements; estimating, by the server computer, afirst characteristic of the antenna system based on the statistic; andtransmitting the first characteristic, by the server computer, to anapplication engine.

A second illustrative method comprises: receiving, by a server computer,i) a first plurality of propagation-time measurements of first signalstransmitted between a first wireless terminal and a base station and ii)a second plurality of propagation-time measurements of second signalstransmitted between a second wireless terminal and the base station,wherein the first and second signals propagate through at least aportion of an antenna system that is communicatively coupled to the basestation; generating a statistic, by the server computer, by applying apredetermined statistical algorithm to a data set, wherein the data setcomprises data points that are based on the first plurality ofpropagation-time measurements and the second plurality ofpropagation-time measurements; estimating, by the server computer, afirst characteristic of the antenna system based on the statistic;estimating, by the server computer, the location of a third wirelessterminal based on the first characteristic of the antenna system,wherein the estimating of the location results in a location estimate;and transmitting, by the server computer, the location estimate to alocation-based application.

A third illustrative method comprises: receiving, by a server computer,a plurality of propagation-time measurements of first signalstransmitted between i) one or more wireless terminals and ii) a basestation, wherein the first signals propagate through at least a portionof a distributed antenna system (DAS) that is communicatively coupled tothe base station, the distributed antenna system comprising at least twoantenna nodes; generating a statistic, by the server computer, byapplying a predetermined statistical algorithm to a data set, whereinthe data set comprises data points that are based on the plurality ofpropagation-time measurements; estimating, by the server computer, afirst characteristic of a first antenna node of the at least two antennanodes, based on the statistic; estimating, by the server computer, thelocation of a first wireless terminal based on the first characteristicof the antenna system, wherein the estimating of the location results ina location estimate; and transmitting, by the server computer, thelocation estimate to a location-based application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a diagram of the salient components of wirelesstelecommunications system 100 in accordance with the illustrativeembodiment of the present invention.

FIG. 2 depicts a diagram of the salient components of wirelesstelecommunications system 100 that provide telecommunications service toat least some of geographic region 220 or that operate within geographicarea 220.

FIG. 3 depicts a diagram of the salient components of wirelesstelecommunications system 100 that provide telecommunications service toat least some of geographic region 320 or that operate within geographicarea 320.

FIG. 4 depicts a diagram of the salient components of cellular basestation 102-1, in communication with wireless terminal 101-1 via atransmission path or paths comprising one or more propagationcomponents.

FIG. 5 depicts a block diagram of the salient components of locationengine 113 in accordance with the illustrative embodiment of the presentinvention.

FIG. 6 depicts a flowchart of the salient processes performed inaccordance with the illustrative embodiment of the present invention.

FIG. 7 depicts a flowchart of the salient processes performed inaccordance with task 607.

FIGS. 8A through 8E depict various probability distributions of variousdata sets.

FIG. 9 depicts a flowchart of the salient processes performed inaccordance with task 609.

FIG. 10 depicts a flowchart of the salient processes performed inaccordance with task 611.

DETAILED DESCRIPTION

Antenna node—For the purposes of this specification, the term “antennanode” and its inflected forms is defined as an antenna element ofmultiple antenna elements within an antenna system (e.g., a distributedantenna system, etc.), in which at least some of the antenna elementsare connected to a common signal source.

Base station—For the purposes of this specification, the phrase “basestation” is defined as a wireless communications station installed at apredetermined (e.g., fixed, etc.) location and used to communicate withone or more wireless terminals via radio.

Based on—For the purposes of this specification, the phrase “based on”is defined as “being dependent on” in contrast to “being independentof”. The value of Y is dependent on the value of X when the value of Yis different for two or more values of X. The value of Y is independentof the value of X when the value of Y is the same for all values of X.Being “based on” includes both functions and relations.

Communicatively coupled—For the purposes of this specification, the term“communicatively coupled” and its inflected forms is defined as beingconnected so as to enable communication with one or more other devices.

Distributed antenna system—For the purposes of this specification, theterm “distributed antenna system” and its inflected forms is defined asa network of spatially separated antenna nodes connected to a commonsignal source via a transport medium that provides wireless servicewithin a geographic area or structure.

Estimate—For the purposes of this specification, the infinitive “toestimate” and its inflected forms (e.g., “estimating”, “estimated”,etc.) should be given the ordinary and customary meaning that the termswould have to a person of ordinary skill in the art at the time of theinvention.

Generate—For the purposes of this specification, the infinitive “togenerate” and its inflected forms (e.g., “generating”, “generation”,etc.) should be given the ordinary and customary meaning that the termswould have to a person of ordinary skill in the art at the time of theinvention.

Location—For the purposes of this specification, the term “location” isdefined as a zero-dimensional point, a finite one-dimensional pathsegment, a finite two-dimensional surface area, or a finitethree-dimensional volume.

Processor—For the purposes of this specification, a “processor” isdefined as hardware or hardware and software that perform mathematicaland/or logical operations.

Propagation time—For the purposes of this specification, “propagationtime” is defined as the length of time it takes for a signal to movealong a transmission path. A measurement related to propagation time canbe time-based; timing-based; delay-based; based on a difference in time,timing, or delay; or based on some combination thereof.

Spatial displacement—For the purposes of this specification, the term“spatial displacement” is defined as the distance along a straight linebetween two points in space.

Statistic—For the purposes of this specification, the term “statistic”is defined as a single measure of some attribute of a sample, calculatedby applying a statistical algorithm to the values of the items of thesample, which are known together as a data set. A “descriptivestatistic” can be used to describe the data in a data set.

Radio—For the purposes of this specification, a “radio” is defined ashardware or hardware and software that is capable of telecommunicationsvia an unguided (i.e., wireless) radio signal of frequency less than 600GHz.

Receive—For the purposes of this specification, the infinitive “toreceive” and its inflected forms (e.g., “receiving”, “received”, etc.)should be given the ordinary and customary meaning that the terms wouldhave to a person of ordinary skill in the art at the time of theinvention.

Transmit—For the purposes of this specification, the infinitive “totransmit” and its inflected forms (e.g., “transmitting”, “transmitted”,etc.) should be given the ordinary and customary meaning that the termswould have to a person of ordinary skill in the art at the time of theinvention.

Wireless network coverage area—For the purposes of this specification,the term “wireless network coverage area” is defined as the geographicarea within which a carrier or a set of equipment, or both, provideswireless service.

Wireless terminal—For the purposes of this specification, the term“wireless terminal” is defined as a device that is capable oftelecommunications without a wire or tangible medium. A wirelessterminal can be mobile or immobile. A wireless terminal can transmit orreceive, or transmit and receive. As is well known to those skilled inthe art, a wireless terminal is also commonly called a cellulartelephone or cellphone, a wireless transmit/receive unit (WTRU), a userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a personal digital assistant (PDA), a smartphone, a smart watch,a computer, or any other type of device capable of operating in awireless environment, for example and without limitation.

FIG. 1 depicts a diagram of the salient components of wirelesstelecommunications system 100 in accordance with the illustrativeembodiment of the present invention. Wireless telecommunications system100 comprises: wireless terminal 101-1, cellular base stations 102-1,102-2, and 102-3, Wi-Fi base stations 103-1 and 103-2, wirelessinfrastructure 111, location-based application server 112, locationengine 113, and GPS constellation 121, interrelated as shown.

Wireless infrastructure 111, location-based application server 112,location engine 113, and Wi-Fi base stations 103-1 and 103-2 are allconnected to one or more interconnected computer networks (e.g., theInternet, a local-area network, a wide-area network, etc.) and, as such,can exchange data in well-known fashion.

Although the illustrative embodiment depicts wireless telecommunicationssystem 100 as comprising only one wireless terminal, it will be clear tothose skilled in the art, after reading this disclosure, how to make anduse alternative embodiments of the present invention that comprise anynumber of wireless terminals 101-1 through 101-M, wherein M is apositive integer.

Wireless terminal 101-1 comprises the hardware and software necessary toperform the processes described below and in the accompanying figures.Furthermore, wireless terminal 101-1 is mobile and can be at anylocation within geographic region 120 at any time.

Wireless terminal 101-1 is capable of providing bi-directional voice,data, and video telecommunications service to a user (not shown), but itwill be clear to those skilled in the art, after reading thisdisclosure, how to make and use embodiments of the present invention inwhich wireless terminal 101-1 provides a different set of services.

In accordance with the illustrative embodiment, wireless terminal 101-1is capable of transmitting one or more radio signals—that can bereceived by one or more of base stations 102-1, 102-2, and 102-3 andWi-Fi base stations 103-1 and 103-2—in accordance with specificparameters (e.g., signal strength, frequency, coding, modulation, timingoffset, etc.), in well-known fashion, and of transmitting at least someof those parameters to location engine 113 as well as other informationdescribed below. Additionally, wireless terminal 101-1 is capable ofreceiving one or more radio signals from each of base stations 102-1,102-2, and 102-3, Wi-Fi base stations 103-1 and 103-2, and GPSconstellation 121, in well-known fashion.

Wireless terminal 101-1 is also capable of identifying each radio signalit receives, in well-known fashion, and of transmitting the identity ofeach signal it receives to location engine 113. Wireless terminal 101-1is further capable of measuring one or more location-dependent traits ofeach radio signal it receives, in well-known fashion, and oftransmitting each measurement it generates to location engine 113.

Cellular base stations 102-1, 102-2, and 102-3 communicate with wirelessinfrastructure 111 via wireline and with wireless terminal 101-1 viaradio in well-known fashion. As is well known to those skilled in theart, base stations are also commonly referred to by a variety ofalternative names such as access points, nodes, network interfaces, etc.Although the illustrative embodiment comprises three cellular basestations, it will be clear to those skilled in the art, after readingthis disclosure, how to make and use alternative embodiments of thepresent invention that comprise any number of cellular base stations.

In accordance with the illustrative embodiment of the present invention,cellular base stations 102-1, 102-2, and 102-3 are terrestrial,immobile, and base station 102-3 is within geographic region 120. Itwill be clear to those skilled in the art, after reading thisdisclosure, how to make and use alternative embodiments of the presentinvention in which some or all of the base stations are airborne,marine-based, or space-based, regardless of whether or not they aremoving relative to the Earth's surface, and regardless of whether or notthey are within geographic region 120.

Cellular base stations 102-1, 102-2, and 102-3 comprise the hardware andsoftware necessary to be 3GPP-compliant and to perform the processesdescribed below and in the accompanying figures. For example and withoutlimitation, each of cellular base stations 102-1, 102-2, and 102-3 arecapable of continually:

-   -   a. receiving one or more radio signals transmitted by wireless        terminal 101-1, and    -   b. identifying each radio signal transmitted by wireless        terminal 101-1, in well-known fashion, and of transmitting the        identity of those signals to location engine 113, and    -   c. measuring one or more location-dependent traits of each radio        signal transmitted by wireless terminal 101-1, in well-known        fashion, and of transmitting the measurements to location engine        113, and    -   d. transmitting one or more signals to wireless terminal 101-1        in accordance with specific parameters (e.g., signal strength,        frequency, coding, modulation, etc.), in well-known fashion, and        of transmitting those parameters to location engine 113.        It will be clear to those skilled in the art how to make and use        cellular base stations 102-1, 102-2, and 102-3.

Wi-Fi base stations 103-1 and 103-2 communicate with wireless terminal101-1 via radio in well-known fashion. Wi-Fi base stations 103-1 and103-2 are terrestrial, immobile, and within geographic region 120.Although the illustrative embodiment comprises two Wi-Fi base stations,it will be clear to those skilled in the art, after reading thisdisclosure, how to make and use alternative embodiments of the presentinvention that comprise any number of Wi-Fi base stations.

Each of Wi-Fi base stations 103-1 and 103-2 are capable of continually:

-   -   a. receiving one or more radio signals transmitted by wireless        terminal 101-1, and    -   b. identifying each radio signal transmitted by wireless        terminal 101-1, in well-known fashion, and of transmitting the        identity of those signals to location engine 113, and    -   c. measuring one or more location-dependent traits of each radio        signal transmitted by wireless terminal 101-1, in well-known        fashion, and of transmitting the measurements to location engine        113, and    -   d. transmitting one or more signals to wireless terminal 101-1        in accordance with specific parameters (e.g., signal strength,        frequency, coding, modulation, etc.), in well-known fashion, and        of transmitting those parameters to location engine 113.

It will be clear to those skilled in the art how to make and use Wi-Fibase stations 103-1 and 103-2.

Wireless infrastructure 111 comprises a switch that orchestrates theprovisioning of telecommunications service to wireless terminal 101-1and the flow of information to and from location engine 113, asdescribed below and in the accompanying figures. As is well known tothose skilled in the art, wireless switches are also commonly referredto by other names such as mobile switching centers, mobile telephoneswitching offices, routers, and so on, for example and withoutlimitation.

Location-based application server 112 comprises hardware and softwarethat uses the estimate of the location of wireless terminal101-1—generated by location engine 113—in one or more location-basedapplications, in well-known fashion. Location-based applications arewell-known in the art and provide services such as, and withoutlimitation, E-911 routing, navigation, location-based advertising, andweather alerts.

Location engine 113 is a data processing system that comprises hardwareand software that generates one or more estimates of the location ofwireless terminal 101-1 as described below and in the accompanyingfigures. It will be clear to those skilled in the art, after readingthis disclosure, how to make and use location engine 113. Furthermore,although location engine 113 is depicted in FIG. 1 as physicallydistinct from wireless infrastructure 111, it will be clear to thoseskilled in the art, after reading this disclosure, how to make and usealternative embodiments of the present invention in which locationengine 113 is wholly or partially integrated into wirelessinfrastructure 111.

FIG. 2 depicts a diagram of the salient components of wirelesstelecommunications system 100 that provide telecommunications service toat least some of geographic region 220 or that operate within geographicarea 220. In particular, wireless terminals 101-1 through 101-M (whereinM as depicted is equal to 7) operate within region 220, and at leastcellular base station 102-1, wireless infrastructure 111, location-basedapplication server 112, and location engine 113 provide service to thewireless terminals and are interrelated as shown. Geographic region 220can be non-overlapping with region 120 or the regions can at leastpartially overlap.

Some are all of wireless terminals 101-1 through 101-M are incommunication with base station 102-1 at any given moment in time.Additionally, some or all of wireless terminals 101-1 through 101-M canalso be in communication with one or more base stations in addition tobase station 102-1.

As discussed above, wireless terminal 101-m, wherein m can have a valueof 1 through M, is further capable of measuring one or morelocation-dependent traits of each radio signal it receives, inwell-known fashion, and of transmitting each measurement it generates tolocation engine 113. At least some of the location-dependent traits arerelated to propagation time, and, in particular, propagation delay insome cases. Some propagation-time-related measurements that can beprovided by terminal 101-m are as follows, for example and withoutlimitation:

-   -   a. the round-trip time (RTT) or round-trip delay time (RTD) of        all of the signals transmitted and receivable by wireless        terminal 101-m through one or more of the base stations.    -   b. the time advance (TA) of all of the signals transmitted and        receivable by wireless terminal 101-m through one or more of the        base stations.    -   c. the received temporal difference of each pair of multipath        components (e.g., one temporal difference for one pair of        multipath components, a pair of temporal differences for a        triplet of multipath components, etc.) of all of the signals        receivable by wireless terminal 101-m from one or more        transmitters.    -   d. the received delay spread (e.g., RMS delay spread, excess        delay spread, mean excess delay spread, etc.) of all of the        signals receivable by wireless terminal 101-m.    -   e. the received relative arrival times of two or more multipath        components of all of the signals receivable by wireless terminal        101-m, from one or more transmitters (which can be determined by        a rake receiver in well-known fashion).

Cellular base station 102-1, as well as other base stations withinsystem 100, is further capable of measuring one or morelocation-dependent traits of each radio signal it receives from one ormore wireless terminals, in well-known fashion, and of transmitting eachmeasurement it generates to location engine 113. At least some of thelocation-dependent traits are related to propagation time, and, inparticular, propagation delay in some cases. Somepropagation-time-related measurements provided by base station 102-1 arethe same as those listed above, for example and without limitation,except that the signal propagation directions are reversed.

By accumulating the aforementioned measurements that are received fromone or more of the wireless terminals or base stations, or both,location engine 113 is capable of performing the tasks described below.

FIG. 3 depicts a diagram of the salient components of wirelesstelecommunications system 100 that provide telecommunications service toat least some of geographic region 320 or that operate within geographicarea 320. In particular, cellular base station 302-1 and antenna nodes303-1 and 303-2 provide service to wireless terminals 101-1 and 101-2,and are interrelated as shown. Geographic region 320 can benon-overlapping with regions 120 and/or 220, or two or more of theregions can at least partially overlap.

Cellular base station 302-1 is similar to cellular base station 102-1 asdescribed above and in FIG. 1. In addition, base station 302-1 supportsa distributed antenna system as is known in the art, depicted as antennasystem 310 comprising antenna nodes 303-1 and 303-2 and cable segments304-1 and 304-2, interconnected as shown. Although a distributed antennasystem is featured in accordance with the illustrative embodiment of thepresent invention, in some embodiments of the present invention adifferent type of antenna system can be used, as those who are skilledin the art will appreciate after reading this specification.Furthermore, as those who are skilled in the art will appreciate afterreading this specification, a different type of distributed antennasystem can be used in which the host base station equipment does nothave its own collocated antenna as does station 302-1.

Although the illustrative embodiment comprises a single base stationthat supports a distributed antenna system, it will be clear to thoseskilled in the art, after reading this disclosure, how to make and useembodiments of the present invention that comprise a different number ofbase stations that support distributed antennas. Furthermore, althoughthe illustrative embodiment comprises two antenna nodes 303-1 and 303-2,it will be clear to those skilled in the art, after reading thisdisclosure, how to make and use embodiments of the present inventionthat comprise a different number of antenna nodes within an antennasystem.

As depicted in FIG. 3, base station 302-1 provides a common signalsource for both antenna nodes 303-1 and 303-2. For example and withoutlimitation, the common signal source can be a radio at the base station.Cable segments 304-1 and 304-2 are part of a transport medium thatprovides a transmit signal from the common source to antenna nodes 303-1and 303-2. Cable segments 304-1 and 304-2 also provide to base station302-1 the signals received from terminals 101-2 and 101-3 by antennanodes 303-1 and 303-2, respectively. Each cable segment exhibits a cabledelay such as an electrical delay along a coax or other type oftransport medium.

FIG. 3 depicts antenna nodes 303-1 and 303-2 in the coverage pattern asshown and with different lengths in the cable segments. As those who areskilled in the art will appreciate, however, after reading thisspecification the antenna nodes can be arranged in a different coveragepattern. For example and without limitation, a plurality of antennanodes can be arranged in a relatively linear pattern (e.g., rectilinear,curvilinear, etc.) such as in a tunnel and/or with a uniform cablelength between contiguous antenna nodes.

FIG. 4 depicts a diagram of the salient components of cellular basestation 102-1, in communication with wireless terminal 101-1 via atransmission path or paths comprising one or more propagationcomponents. Cellular base station 102-1 comprises: one or more antennaelements 301 and base station processing equipment 402, which comprisesone or more radios 403. Signal path 404 between antenna element 401 andradio 403, or between element 401 and a different base station equipmentcomponent, is characterized by a first propagation delay component thatis attributed to the type and length of transmission medium used (e.g.,cable, etc.).

As those who are skilled in the art will appreciate after reading thisspecification, signal path 404 might instead or in addition span thetransport medium (e.g., cable segment 304-1, etc.) between an antennanode (e.g., node 303-1, etc.) and a base station component, such as aradio.

Additionally, there are one or more signal paths taken by a signaltransmitted between antenna element 401 and wireless terminal 101-1.Signal path 405, which is a direct path, is characterized by a secondpropagation delay component; signal path 406, which is an indirect pathdue to reflection off of building 411, is characterized by a secondpropagation delay component; and signal path 407, which is an indirectpath due to reflection off of mountain 412, is characterized by a thirdpropagation delay component. As those who can appreciate after readingthis specification, other signal paths can occur based on reflectionfrom other terrestrial objects and from bodies of water, and onphenomena other than reflection. When radio signals reach a receivingantenna by two or more signal paths, multipath is said to occur.

Wireless terminal 101-1 and/or base station 102-1 are capable of makingand providing (e.g., to location engine 113, etc.) propagation-timemeasurements, in which the measurements reflect at least some of thepropagation delay components described above.

FIG. 5 depicts a block diagram of the salient components of locationengine 113 in accordance with the illustrative embodiment. Locationengine 113 comprises: processor 501, memory 502, and receiver andtransmitter 503, which are interconnected as shown. In accordance withthe illustrative embodiment of the present invention, location engine113 is a server computer. As those who are skilled in the art willappreciate after reading this specification, however, location engine113 can be a different type of data-processing system or computingdevice.

Processor 501 is a general-purpose processor that is configured toexecute an operating system and the application software that performsthe operations described herein, including the operations described inFIG. 6 and other figures. Processor 501 is also capable of populating,amending, using, and managing propagation-time measurements, data setsbased on the measurements, statistics of each data set, and so on. Itwill be clear to those skilled in the art how to make and use processor501.

Memory 502 is a non-volatile memory that is configured to store:

-   -   a. operating system 511, and    -   b. application software 512, and    -   c. database 513 for storing one or more data sets as described        below.        It will be clear to those skilled in the art how to make and use        memory 502.

Receiver and transmitter 503 is configured to enable location engine 113to receive from and transmit to wireless terminal 101-m, wirelessinfrastructure 111, location-based application server 112, and the basestations (i.e., cellular and WiFi), in well-known fashion. It will beclear to those skilled in the art how to make and use receiver andtransmitter 503.

Operation of the Illustrative Embodiment—FIG. 6 depicts a flowchart ofthe salient processes performed in accordance with the illustrativeembodiment of the present invention.

The processes performed by wireless telecommunications system 100 of theillustrative embodiment are depicted in the drawings (i.e., FIG. 6 andsubsequent figures) as being performed in a particular order. It will,however, be clear to those skilled in the art, after reading thisdisclosure, that such operations can be performed in a different orderthan depicted or can be performed in a non-sequential order (e.g., inparallel, etc.). In some embodiments of the present invention, some orall of the depicted processes might be combined or performed bydifferent devices, either within location engine 113 or other thanlocation engine 113. In some embodiments of the present invention, someof the depicted processes might be omitted.

For purposes of clarity, wireless terminal 101-1 and cellular basestation 302-1 are used as examples of a wireless terminal and basestation. Station 302-1 acts as a host of distributed antenna system(DAS) 310 through at least a portion of which signals transmittedbetween one or more wireless terminals and the base station propagate.However, as those who are skilled in the art will appreciate afterreading this specification, at least some of the tasks described beloware applicable to other wireless terminals and other base stations(e.g., WiFi, etc.) as well.

At task 601, location engine 113 receives one or more propagation-timemeasurements (e.g., round-trip time, etc.), wherein each measurement isthat of a signal in a transmission between a wireless terminal (e.g.,terminal 101-1, etc.) and base station 302-1. Measurements can bereceived for signals between multiple wireless terminals and a givenbase station, for signals between a given wireless terminal and multiplebase stations, and for signals across multiple paths between eachwireless terminal and base station, in any combination thereof. Themeasurements can be representative of signals from a base station to awireless terminal, or from a wireless terminal to a base station, orboth. In some embodiments of the present invention, a propagation-timemeasurement can be received in response to location engine 113transmitting a mobile-terminated location request (MTLR) message, orequivalent.

The propagation-time measurements actually received by location engine113 are based on the propagation-time-related measurements provided byterminal 101-1 as described above and in FIG. 2. In some embodiments ofthe present invention, one or more of the propagation-time measurementsreceived by location engine 113 are further based on a predeterminedconstant. For example and without limitation, a wireless serviceprovider in control of system 100 might choose to adjust (i.e., by a“fudge factor”) one or more of the measurements provided by wirelessterminal 101-1, in order to compensate for known signal paths within theequipment itself, such as signal path 404 that is characterized by afirst propagation delay component. In this example, the service providermight attempt to correct by subtracting out the delay effects introducedby signal path 404, in order to obtain a measurement that is morerepresentative of one or more signal paths between an antenna element(e.g., node 303-1, node 303-2, element 401, etc.) and wireless terminal101-1, instead of between radio 403 and the wireless terminal.

Location engine 113 also can receive evidence of the location of one ormore wireless terminals, such as terminal 101-1. Evidence of a locationis data to which a location estimation algorithm can be applied in orderto generate an estimated location (e.g., a geographic location, etc.).For example and without limitation, evidence of the location cancomprise a signal-strength measurement, a time-related measurement, orinformation that, by itself, is not a representation of the geographiclocation of a wireless terminal, estimated or otherwise, but that isprobative of the geographic location. In some alternative embodiments ofthe present invention, the evidence of a location can comprise arelatively coarse location, whereas the estimated location generatedfrom the evidence can be a relatively fine location. The evidence of thelocation can be different from and independent of the propagation-timemeasurements, while concurrently the location to which the evidenceapplies can be coincident with the location at which and/or timeinterval during which the propagation-time characteristic was measuredand/or reported.

Location engine 113 also can receive evidence of the location of one ormore of the base stations, such as base station 302-1. In someembodiments, location engine 113 receives a geographic location of oneor more of the base stations, in which the location or locations havebeen confirmed to a known degree of accuracy.

At task 603, in some embodiments of the present invention, locationengine 113 estimates the geographic location of wireless terminal 101-1based on the received evidence of the location of terminal 101-1,thereby establishing a “ground truth” for the location of the terminal.Engine 113 can estimate the location of other wireless terminals aswell, thereby also establishing ground truths for those terminals. Thereare various techniques that can be used to estimate the location ofwireless terminal 101-1 based on the received evidence. See for exampleand without limitation, U.S. Pat. Nos. 6,944,465, 7,460,505, 7,383,051,7,257,414, 7,753,278, 7,433,695, 7,848,762, and 8,630,665, each of whichis incorporated by reference herein. Location engine 113, in someembodiments of the present invention, can receive an estimate of thegeographic location of wireless terminal 101-1 in which the estimate hasbeen calculated elsewhere (e.g., by wireless terminal 101-1 itself,etc.). In some embodiments of the present invention, the uncertaintiesof one or more grounds truths are included as a component of theanalysis represented by method 500.

At task 605, in some embodiments of the present invention, locationengine 113 estimates a spatial displacement (e.g., shortest distance,etc.) between wireless terminal 101-1 and base station 302-1 based onthe estimated location of terminal 101-1. Engine 113 can estimate thespatial displacements between other combinations of wireless terminalsand base stations as well. In some embodiments of the present invention,evidence of the location of base station 302-1, the location itself ofbase station 302-1, or the location of an antenna element (e.g., node303-1, node 303-2, element 401, etc.) is also used in estimating thespatial displacement.

At task 607, location engine 113 generates one or more statistics of adata set, in which the data set comprises data points that are based onat least some of the propagation-time measurements received inaccordance with task 601. Task 607 is described in detail below and inFIG. 7.

At task 609, location engine 113 estimates one or more characteristicsof antenna system 310 hosted by base station 302-1, based on thestatistic generated at task 607. Task 609 is described in detail belowand in FIG. 9. In some embodiments, location engine 113 estimates theone or more characteristics based on the spatial displacement ordisplacements estimated at task 605.

At task 611, location engine 113 estimates the location of a wirelessterminal based on one or more of the characteristics estimated at task609. Task 611 is described in detail below and in FIG. 10.

At task 613, location engine 113 transmits the location estimate thatwas made available at task 611, to a location application at applicationserver 112. In some embodiments of the present invention, engine 113transmits the location estimate to a device different from server 112 oruses the location estimate for its own purposes. In some otherembodiments of the present invention, engine 113 transmits the one ormore characteristics of the antenna system made available at task 609,to a device (e.g., an application engine, etc.) or uses thecharacteristics for its own purposes.

Location engine 113 then repeats one or more of the afore-describedtasks.

Task 607: Generate a Statistic—FIG. 7 depicts a flowchart of the salientprocesses performed in accordance with task 607.

At task 701, location engine 113 optionally conditions thepropagation-time measurement received at task 601, resulting in aconditioned value. In accordance with the illustrative embodiment of thepresent invention, conditioning the propagation-time measurementcomprises converting the received measurement to a different measurementunit and/or to a different frame of reference. For example and withoutlimitation, the propagation-time-related value can be converted to atime-related value that is more convenient to work with, such as bytaking a round-trip-time (RTT) measurement, in chips, and converting itto a value in nanoseconds. As another example, an RTT measurement can beconverted to a one-way measurement representation, instead of around-trip representation.

In accordance with some embodiments of the present invention, theconditioning can comprise a calculation of the difference between thepropagation-time measurement and a second value after they have beennormalized or converted into comparable units of measure.

In regard to wireless propagation components 405 through 407 in FIG. 4,in some embodiments of the present invention the conditioned value mightbe adjusted in order to account for the probability of thepropagation-time measurement not being representative of a direct-pathradio signal, but of the measurement being influenced by anindirect-path or a multipath radio signal.

At task 703, location engine 113 stores the conditioned value, in memory502's database, in order to build a data set, such as one of the datasets depicted in FIGS. 8A through 8E described below.

At task 705, location engine 113 repeats afore-described tasks 701 and703 in order to ensure that number of values that constitute the dataset is sufficient. FIG. 8A depicts a probability distribution 800 ofdata set 801, developed as a histogram of multiple conditioned valuesgenerated at task 701, which are being stored into memory at task 703.Data set 801 can comprise conditioned values that are representativeonly of a single wireless terminal/base station pair, representative ofmultiple wireless terminals with respect to a single base station,representative of one or more wireless terminals with respect tomultiple base stations, and so on.

Some characteristics of data sets are discussed here. First, data set801 extends over to the left side of the y-axis. One situation in whichthis can occur is when the service provider has overcorrected, in thepropagation-time measurement data delivered to location engine 113, forelectrical delays in the equipment (e.g., cabling, antenna amplifiers,etc.) that are present in path 404 of FIG. 4. The overcorrection mightbe even greater, as depicted by probability distribution 810 of data set811 in FIG. 8B. On the other hand, the overcorrection might be small ornon-existent, as depicted by probability distribution 820 of data set821 in FIG. 8C. As those who are skilled in the art will appreciateafter reading this specification, the relative position of the data setalong the x-axis can be used to indicate or suggest that the cable delaycompensation is too high, too low, or proper.

Second, the depicted data set exhibits some positive skewness (i.e.,skewness to the right). One situation in which this can occur is whensome multipath is present in the coverage area or areas from which thedata originates. Alternatively, there might be little or no skewness, asdepicted by probability distribution 830 of data set 831 in FIG. 8D. Asthose who are skilled in the art will appreciate after reading thisspecification, the skewness of the data set can be used to indicate orsuggest a condition existing in the coverage area, such as multipath, aswell as the degree to which the condition exists (e.g., high amount, lowamount, non-existent, etc.).

The conditioned values that constitute the data sets can depend onvarious factors. For example and without limitation, data set 801 mightbe developed from conditioned values in which some or all of the basestations, in a predetermined group of base stations, are represented inthose constituent conditioned values, if one of more of the followingapply:

-   -   a. similar radio-frequency (RF) propagation conditions (e.g.,        multipath, etc.) are present in the coverage areas of the base        stations.    -   b. similar base station equipment configurations (e.g.,        sectorization, etc.) exist.    -   c. similar propagation-time corrections made by the service        provider are in effect.        On the other hand, data set 801 might instead be developed from        conditioned values in which only a single base station, or a        limited group of similar base stations, is represented in those        constituent conditioned values, if one or more of the following        apply:    -   a. different RF propagation conditions are present.    -   b. different base station equipment configurations exist.    -   c. different corrections made by the service provider are in        effect.

In regard to a distributed antenna system, FIG. 8E depicts a probabilitydistribution 840 of data set 841, developed as a histogram of multipleconditioned values generated at task 701, which are being stored intomemory at task 703. In this probability distribution, there are twodistinct groupings of values, grouping 841-1 and 841-2. Each groupingcorresponds to a different antenna node that constitutes the antennasystem. For example, grouping 841-1 can correspond to antenna node 303-1and grouping 841-2 can correspond to antenna node 303-2 in FIG. 3. Theexistence of the two groupings, as well as their characteristics, can beused to identify or suggest one or more characteristics of the antennasystem, as described later.

At task 705, location engine 113 determines when a sufficient number ofconditioned values have been accumulated as part of the data set. Itwill be clear to those who are skilled in the art after reading thisspecification, how to determine when a sufficient number has beenaccumulated. This might depend, for example, one or more sources oferror such as the quantization error of the propagation-time (e.g., RTT,etc.) measurements made by the wireless terminals.

At task 707, location engine 113 selects one or more statisticalalgorithms whose resulting statistical values are to be determined withrespect to one or more of the values in the data set being accumulated,which, for pedagogical purposes, is data set 841 that corresponds to adistributed antenna system. In some embodiments of the presentinvention, a to-be-determined statistic can be a descriptive statistic,in which case the statistic can be summary statistic or can be based ona summary statistic. Summary statistics include, while not being limitedto:

-   -   a. the number of local groupings of data in data set 841 (e.g.,        grouping 841-1, etc.), each grouping corresponding to a local        maximum in the data set    -   b. for one or more of the local groupings, a measure of location        within data set 841—arithmetic mean, median, mode, interquartile        mean, a predetermined percentile, etc.    -   c. for one or more of the local groupings, a measure of        statistical dispersion within data set 841—standard deviation,        variance, range, interquartile range, absolute deviation,        distance standard deviation, etc.    -   d. for one or more of the local groupings, a measure of the        shape of the distribution—skewness, distance skewness, etc.

As those who are skilled in the art will appreciate after reading thisspecification, the statistic can be selected based on one or more of:the RF environment (e.g., multipath that is present, etc.), the basestation or stations involved (i.e., transmitting and/or receivingsignals), the wireless terminal or terminals involved (i.e.,transmitting and/or receiving signals), any correction or offset appliedby the service provider, or trial-and-error, for example and withoutlimitation.

At task 709, location engine 113 generates a first statistic by applyingone or more corresponding, predetermined statistical algorithms to adata set, in well-known fashion. In some embodiments, engine 113 canadjust the generated statistic accordingly or calculate a value of anadditional statistic or characteristic of data set 841 based on thefirst statistic. For example and without limitation, if the skewness ofdata set 841 indicates the presence of strong multipath (i.e., adistinct, positive skewness is observed), then the characteristic ofdata set 841 for which a value is calculated and eventually provided totask 609 might be a first characteristic. However, if the skewness ofdata set 841 indicates the presence of weak or no multipath (i.e., aslight skewness or no skewness is observed), then the characteristic ofdata set 841 for which a value is calculated and eventually provided totask 609 might be a second characteristic. As multipath might varysignificantly from one cell of coverage to another, the mere presence ofskewness might dictate that separate data sets be maintained andanalyzed for each base station.

After task 709, control of task execution then proceeds to task 609.

As those who are skilled in the art will appreciate after reading thisspecification, a representation of a data set can be used that isalternative to the probability distribution representations depicted inFIGS. 8A through 8E. Moreover, a method of calculating a correction canbe used that is alternative to generating a statistic of a data set.

Task 609: Estimate a Characteristic—FIG. 9 depicts a flowchart of thesalient processes performed in accordance with task 609.

At task 901, location engine 113 identifies whether antenna system 310corresponding to data set 841 is a distributed antenna system. Based onhaving determined, at task 709, the number of local maxima in data set841 to be greater than one, engine 113 uses that statistic to infer thatmore than one antenna node exists in antenna system 310 and,accordingly, that the antenna system is a distributed antenna system.Engine 113 provides this result as a characteristic value.

At task 903, location engine 113 identifies the number of nodes in thedistributed antenna system identified as such. Based on havingdetermined, at task 709, the number of local maxima in data set 841,engine 113 uses that statistic to infer the number of antenna nodes.Engine 113 provides this result as a characteristic value.

At task 905, location engine 113 estimates a cable delay between apredetermined antenna node in the distributed antenna system identifiedas such and a predetermined component base station 302-1. Based onhaving determined, at task 709, the position of a local maximum (e.g.,the leftmost in the data set, etc.) in data set 841 that corresponds tothe predetermined antenna node of interest (e.g., node 303-1 closest tobase station 302-1, etc.), engine 113 uses that statistic to estimatethe cable delay. Engine 113 provides this result as a characteristicvalue.

At task 907, location engine 113 estimates whether a predeterminedantenna node in the distributed antenna system identified as such isserving a first wireless terminal. Based on having determined, at task709, the position of a local maximum (e.g., the leftmost in the dataset, etc.) in data set 841 that corresponds to the predetermined antennanode of interest (e.g., node 303-1 closest to base station 302-1, etc.),engine 113 uses that statistic against which to compare one or morepropagation-time measurements received for the first wireless terminal(i.e., measured by the first terminal and/or base station serving thefirst terminal). Based on the comparison, location engine 113 inferswhether the antenna node is serving the first terminal. For example andwithout limitation, the inference can be based on the propagation-timemeasurement's closeness, relative position to, etc. the local maximum ofthe antenna node's data grouping in data set 841. Engine 113 providesthis result as a characteristic value.

After task 907, control of task execution then proceeds to task 611.

Task 611: Estimate the Location—FIG. 10 depicts a flowchart of thesalient processes performed in accordance with task 611. In general,location engine 113 can determine the location of the wireless terminalin the following manner. Once the characteristic is made available attask 609, engine 113 can use that characteristic, or a secondcharacteristic based on the first characteristic, to further adjust eachpropagation-time measurement being reported so that the propagation-timemeasurement can be directly used in a meaningful way to determinelocation. The adjusted and improved propagation-time measurement canthen be directly used as part of one or more well-known techniques forlocation determination (e.g., OTDOA, Cell ID+RTT, etc.), in order toprovide a location estimate that represents an improvement over alocation estimate obtained by using the unadjusted measurements.

At task 1001, location engine 113 adjusts one or more propagation-timemeasurements based on the cable delay estimated at task 905. For exampleand without limitation, engine 113 can subtract the cable delay from themeasurement, in order to provide an adjusted propagation-timemeasurement that is more representative of a propagation-timecharacteristic between the wireless terminal and the antenna nodeitself.

At task 1003, location engine 113 infers evidence of a location ofwireless terminal 101-1 based on the cable delay estimated at task 905.For example and without limitation, if the distance implied by areceived propagation-time measurement is small relative to the cabledelay between a base station (e.g., station 302-1, etc.) and a remote,distributed antenna element (e.g., node 303-1, etc.), then the radiatingsource of the signal must be the base station's collocated antenna,thereby making one or more possible locations associated with thedistributed antenna improbable. As another example, if the distanceimplied by a received propagation-time measurement exceeds the maximumdistance associated with a particular antenna, then the radiating sourceof the signal must not be that antenna. This is because the distanceimplied by the received propagation-time measurement exceeds the maximumdistance at which a signal radiated from an antenna collocated with thebase station might be expected to be detectable, thereby making one ormore possible locations associated with the base station's antennaimprobable.

At task 1005, location engine 113 marks the antenna node identified as aserving antenna node of wireless terminal 101-1. This, in and of itself,provides evidence of location that can be used to generate a locationestimate.

At task 1007, location engine 113 designates at least one of a pluralityof possible locations of the wireless terminal 101-1 as improbable basedon whether an antenna node is estimated to be serving first wirelessterminal, such as the serving antenna node marked as such at task 1005.In some embodiments, location engine 113 can designate at least one of aplurality of possible locations of the wireless terminal 101-1 asimprobable based on the outcome of task 1003. This designation of one ormore possible locations as improbably is part of a process referred toas “search area reduction,” which is now explained.

Depending on the location technique being used, without search areareduction all of the locations in geographic region 320 would have to beconsidered as candidates because, prior to process 1007, wirelessterminal 101-1 could be in any location out of possibly thousands,millions, or billions of locations. Therefore, to expedite theperformance of certain tasks, location engine 113 can perform one ormore computationally efficient tests that quickly and summarilyeliminate many possible locations for wireless terminal 101-1 fromconsideration, and, therefore, summarily set to zero the probabilitythat wireless terminal 101-1 is at those locations. This reduces thenumber of locations that would otherwise have to be fully considered andgenerally improves the speed with which certain tasks are performed.

In accordance with the illustrative embodiment, one such test comprisesthe actions performed in accordance with task 1007. For example andwithout limitation, the probability that wireless terminal 101-1 is atthe locations associated with an antenna node can be set to zero if theantenna node is not considered to be a serving antenna node. For moredetails in regard to search area reduction, see for example and withoutlimitation, U.S. Pat. Nos. 6,944,465, 7,460,505, 7,383,051, 7,257,414,7,753,278, 7,433,695, 7,848,762, and 8,630,665, each of which isincorporated by reference herein.

At task 1009, location engine 113 generates a location estimate of thegeographic location of wireless terminal 101-1, based on the resultsfrom one or more of tasks 1001, 1003, 1005, and 1007. There are varioustechniques that can be used to estimate the location of wirelessterminal 101-1 based on the results from the afore-listed tasks. See,for example and without limitation, one or more of the aforementionedU.S. patents. In some embodiments of the present invention, locationestimation techniques other those described in the aforementioned U.S.patents can instead be used, as those who are skilled in the art willappreciate after reading this specification.

Location engine 113, in some embodiments of the present invention, canreceive an initial estimate of the geographic location of wirelessterminal 101-1 in which the initial estimate has been calculatedelsewhere (e.g., by wireless terminal 101-1 itself, etc.) and can thenapply the results from the afore-listed tasks in order to generate anupdated estimate. In some embodiments of the present invention, theuncertainties of one or more grounds truths estimated at task 603 can beconsidered in generating the location estimate.

In accordance with the illustrative embodiment of the present invention,engine 113 estimates the location of a wireless terminal different fromthe one or more wireless terminals for which propagation-timemeasurements have been received at task 601. In some embodiments of thepresent invention, engine 113 refines the estimate of the location ofone or more wireless terminals for which the propagation-timemeasurements have been received. In some other embodiments, locationengine 113 estimates the location based on the spatial displacement ordisplacements estimated at task 605 and/or the statistic or statisticsgenerated at task 607 and/or the characteristic or characteristicsgenerated at task 609. As a result of this task, engine 113 makesavailable a location estimate of the wireless terminal.

In some embodiments of the present invention, the location estimate isbased on concurrent or simultaneous propagation-time measurementsbetween a wireless terminal and more than one base station. For example,analysis of the correlated measurements can add to the precision of theestimate.

It is to be understood that the disclosure teaches just one example ofthe illustrative embodiment and that many variations of the inventioncan easily be devised by those skilled in the art after reading thisdisclosure and that the scope of the present invention is to bedetermined by the following claims.

What is claimed is:
 1. A method comprising: receiving, by a server computer, a plurality of propagation-time measurements of first signals transmitted between i) one or more wireless terminals and ii) a base station, wherein the first signals propagate through at least a portion of an antenna system that is communicatively coupled to the base station, and wherein the antenna system is a distributed antenna system; generating a statistic, by the server computer, by applying a predetermined statistical algorithm to a data set, wherein the data set comprises data points that are based on the plurality of propagation-time measurements; estimating, by the server computer, a first characteristic of the antenna system based on the statistic, wherein the first characteristic is cable delay between a first antenna node in the distributed antenna system and a predetermined component of the base station, and wherein the estimating of the first characteristic is based on the position of a first local maximum in the data set; and transmitting the first characteristic, by the server computer, to an application engine.
 2. The method of claim 1 wherein each of the plurality of propagation-time measurements is based on at least one of i) a round-trip time (RTT) measurement and ii) a timing advance (TA) measurement.
 3. The method of claim 1 wherein the first characteristic identifies whether the antenna system is a distributed antenna system comprising at least two antenna nodes.
 4. The method of claim 1 further comprising identifying, by the server computer, the number of antenna nodes in the distributed antenna system based on the statistic having identified the number of local maxima in the data set.
 5. The method of claim 1 further comprising: receiving a propagation-time measurement of a second signal transmitted between a first wireless terminal and the base station; and estimating the location of the first wireless terminal based on i) the cable delay and ii) the propagation-time measurement of the second signal.
 6. The method of claim 1 further comprising estimating, based on the position of the first local maximum in the data set, whether the first antenna node in the distributed antenna system is serving a first wireless terminal.
 7. The method of claim 6 further comprising estimating the location of the first wireless terminal based on whether the first antenna node is estimated to be serving the first wireless terminal.
 8. The method of claim 7 wherein the estimating of the location of the first wireless terminal is further based on designating at least one of a plurality of possible locations of the first wireless terminal as improbable based on whether the first antenna node is estimated to be serving first wireless terminal.
 9. A method comprising: receiving, by a server computer, i) a first plurality of propagation-time measurements of first signals transmitted between a first wireless terminal and a base station and ii) a second plurality of propagation-time measurements of second signals transmitted between a second wireless terminal and the base station, wherein the first and second signals propagate through at least a portion of an antenna system that is communicatively coupled to the base station, and wherein the antenna system is a distributed antenna system; generating a statistic, by the server computer, by applying a predetermined statistical algorithm to a data set, wherein the data set comprises data points that are based on the first plurality of propagation-time measurements and the second plurality of propagation-time measurements; estimating, by the server computer, a first characteristic of the antenna system based on the statistic, wherein the first characteristic is cable delay between a first antenna node in the distributed antenna system and a predetermined component of the base station, and wherein the estimating of the first characteristic is based on the position of a first local maximum in the data set; estimating, by the server computer, the location of a third wireless terminal based on the first characteristic of the antenna system, wherein the estimating of the location results in a location estimate; and transmitting, by the server computer, the location estimate to a location-based application.
 10. The method of claim 9 wherein each of the first plurality of propagation-time measurements is based on at least one of i) a round-trip time (RTT) measurement and ii) a timing advance (TA) measurement.
 11. The method of claim 9 wherein the first characteristic identifies whether the antenna system is a distributed antenna system comprising at least two antenna nodes, and wherein the estimating of the location is further based on the value of the first characteristic.
 12. The method of claim 9 wherein the estimating of the location is further based on the cable delay.
 13. The method of claim 9 further comprising: receiving, by the server computer, a propagation-time measurement of a third signal transmitted between the third wireless terminal and the base station, wherein the estimating of the location is further based on the propagation-time measurement of the third signal.
 14. The method of claim 9 further comprising estimating, based on, the position of the first local maximum in the data set, whether the first antenna node in the distributed antenna system is serving the third wireless terminal, wherein the estimating of the location is further based on whether the first antenna node is serving the third wireless terminal.
 15. The method of claim 14 wherein the estimating of the location is further based on designating at least one of a plurality of possible locations of the third wireless terminal as improbable based on the estimating of whether the first antenna node is serving the third wireless terminal.
 16. A method comprising: receiving, by a server computer, a plurality of propagation-time measurements of first signals transmitted between i) one or more wireless terminals and ii) a base station, wherein the first signals propagate through at least a portion of a distributed antenna system (DAS) that is communicatively coupled to the base station, the distributed antenna system comprising at least two antenna nodes; generating a statistic, by the server computer, by applying a predetermined statistical algorithm to a data set, wherein the data set comprises data points that are based on the plurality of propagation-time measurements; estimating, by the server computer, a first characteristic of a first antenna node of the at least two antenna nodes, based on the statistic, wherein the first characteristic is cable delay between the first antenna node in the distributed antenna system and a predetermined component of the base station, and wherein the estimating of the first characteristic is based on the position of a first local maximum in the data set; estimating, by the server computer, the location of a first wireless terminal based on the first characteristic of the antenna system, wherein the estimating of the location results in a location estimate; and transmitting, by the server computer, the location estimate to a location-based application.
 17. The method of claim 16 wherein each of the plurality of propagation-time measurements is based on at least one of i) a round-trip time (RTT) measurement and ii) a timing advance (TA) measurement.
 18. The method of claim 16 wherein the estimating of the location is further based on the cable delay.
 19. The method of claim 16 further comprising receiving, by the server computer, a propagation-time measurement of a second signal transmitted between the first wireless terminal and the base station, wherein the estimating of the location is further based on the propagation-time measurement of the second signal.
 20. The method of claim 16 further comprising estimating, based on the position of the first local maximum in the data set, whether the first antenna node in the distributed antenna system is serving the first wireless terminal, wherein the estimating of the location is further based on whether the first antenna node is serving the first wireless terminal.
 21. The method of claim 20 wherein the estimating of the location is further based on designating at least one of a plurality of possible locations of the first wireless terminal as improbable based on the estimating of whether the first antenna node is serving the first wireless terminal. 